基于HITRAN数据库的深海甲烷辐射光谱仿真研究

研发能够精确、实时、原位获取热液甲烷数据的深海甲烷传感器对深海研究具有非常重要的意义。前期研制的两款深海甲烷光学成像干涉系统,均利用甲烷辐射光谱开展甲烷状态参数探测和反演。首先,以分子光谱辐射理论为基础,建立了分子辐射光谱与浓度、温度、压强的理论关系式,结合深海高压环境特点,建立了基于Lorentz线型的深海分子辐射模型,该模型为利用光谱法定量反演分子浓度、温度、压强等状态参数提供理论依据,同时为深海分子光谱仿真提供有力工具。接着,借助HITRAN分子光谱数据库提供的分子基本谱线参数,挑选出甲烷成像干涉系统的光源谱线。对比CH₄分子与CO₂, H₂S, H₂O等分子的特征吸收谱线,在5 990～6 150 cm-1波段范围内,CH₄谱线强度比CO₂, H₂S, H₂O等三种干扰分子的谱线强度约高2～3个数量级,且此波段内甲烷六条有效谱线分布均匀,谱线间距皆约为2～3 nm,非常适合采用光谱法进行分子状态参数探测,因此选择谱线干扰较弱、谱线分布均匀、谱线间距适中的甲烷六条谱线(1 640.37, 1 642.91, 1 645.56, 1 648.23, 1 650.96和1 653.72 nm)作为甲烷成像干涉探测系统的目标光源谱线。最后,基于深海分子辐射模型和HITRAN数据库的甲烷分子基本谱线参数,人工合成了甲烷任意浓度,任意温度和任意压强的辐射光谱数据,并分析了甲烷辐射光谱随浓度、温度和压强的变化特征。对于单一中心谱线,甲烷分子辐亮度随着浓度的升高而线性增大,随着温度的升高而非线性增大,随着压强的升高而非线性减小。对于全波段谱线,甲烷辐射光谱的全线宽随着浓度、温度的升高而变宽,随着压强的升高而变窄。建立的深海甲烷辐射光谱理论和仿真分析结果,可以为基于光谱法的海洋原位甲烷传感器的研制和数据反演提供数据支撑和理论依据。     

Spin-Polarized Transport through the T-Shaped Double Quantum Dots with Fano-Kondo Interaction

We theoretically investigate the spin-polarized transport properties of the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We calculate the density of states and the liner conductance in this system with both parallel and antiparallel lead-polarization alignments, and our results show that the transport properties of this system depend on both the tunnelling strength between the two dots and the spin-polarized strength p. This system is a possible candidate for spin valve transistors in the spintronics.     

Si4团簇电子输运性质的第一性原理计算

采用密度泛函理论和非平衡格林函数相结合的方法对Si₄ 团簇与Au(100)电极空位相连的纳米结点的电子输运性质进行了理论模拟计算, 得到了纳米结点在不同距离下的几何结构、电子结构、电导、透射谱、电荷转移量; 讨论了当距离d_z=12.004 Å时纳米结点的电导、电流随电压的变化关系. 关键词： 密度泛函理论 非平衡格林函数 4团簇')" href="#">Si₄团簇 电子输运     

Spin-polarized transport through the T-shaped double quantum dots

Using the Keldysh nonequilibrium Green function and equation-of-motion technique, this paper investigates the spin-polarized transport properties of the T-shaped double quantum dots （DQD） coupled to two ferromagnetic leads. There are both Fano effect and Kondo effect in the system, and due to their mutual interaction, the density of states, the current, and the differential conductance of the system depend sensitively on the spin-polarized strength. Thus the obtained results show that this system is provided with excellent spin filtering property, which indicates that this system may be a candidate for spin valve transistors in the spintronics.     

Au-Si-Au结点电子输运性质的第一性原理计算

采用密度泛函理论和非平衡格林函数相结合的方法对Au(100)-Si-Au(100) 系统左侧对顶位、右侧对空位的纳米结点的电子输运性质进行了理论模拟计算, 结果得到纳米结点的电导随电极距离(d_z)增大而减小. 在d_z =9.72 Å时, 结点的结合能最低, 结构最稳定, 此时电导为1.227G₀ (G₀=2e²/h), 其电子输运通道主要是Si原子的p_x, p_y和 p_z轨道电子形成的最高占居轨道共振峰; 在外偏压下, 电流-电压曲线表现出线性特征; 随着外加正负电压的增大, 电导略有减小, 且表现出不对称性的变化. 关键词： 硅原子 电子输运 密度泛函理论 非平衡格林函数     

Majorana–Kondo interplay in a Majorana wire-quantum dot system with ferromagnetic contacts*

We consider a single-level quantum dot(QD)and a topological superconducting wire hosting Majorana bound states at its ends.By the equation of motion method,we give the analytical Green’s function of the QD in the noninteracting and the infinite interacting case.We study the effects of QD energy level and the spin polarization on the density of states(DOS)and linear conductance of the system.In the noninteracting case,the DOS resonance shifts with the change of energy level and it shows bimodal structure at large spin polarization strength.In the infinite interacting case,the up-spin linear conductance first increases and then decreases with the increase of spin polarization strength,but the down-spin is stable.However,the DOS shows a splitting phenomenon in the large energy level with the increase of spin polarization strength.This provides an interesting way to explore the physical properties of such spin dependent effect in the hybrid Majorana QD systems.     

Hybridization Induced Competitive Scanning Tunneling Interference Process into a Heavy Fermion System

We theoretically present the results for a scanning interference tunneling process between a metallic tip and a heavy fermion system. The density of states(DOS) and the differential conductance at zero temperature under different c-f band hybridizations, as well as the interference Fano ratio strength in the heavy fermion system,are calculated. It is found that the hybridization strength gives rise to the splitting effect in the DOS around the Fermi energy. Also the interference Fano ratio strength makes the differential conductance characteristics strongly asymmetric.     

硅纳米结点电子输运性质的计算

运用第一性原理密度泛函理论结合非平衡格林函数方法,对3个Si原子构成的直线链耦合在Au(100)面形成的三明治结构的纳米结点的电子输运进行计算.结果得到结点电导随距离的变化,当d_z=1.584 nm时,结合能最小,结构最稳定,此时Si-Si键长为0.216 nm,Si-Au键长为0.227 nm,电导为0.729 G₀(G₀=2e²/h),其电子传输通道主要由Si原子的p_x、p_y轨道电子构成;随着外电压的增大,结点的电导减小,而其I-V曲线表现出线性特征.     

Fano--Kondo effect in the T-shaped double quantum dots coupled to ferromagnetic leads

Using an equation-of-motion technique, we theoretically study the Fano--Kondo effect in the T-shaped double quantum dots coupled to two ferromagnetic leads by the Anderson Hamiltonian. We calculate the density of states in this system with both parallel and antiparallel lead-polarization alignments, and our results reveal that the interdot coupling, the spin-polarized strength and the energy level of the side coupled quantum dot greatly influence the density of states of the central quantum dot. This system is a possible candidate for spin valve transistors and may have potential applications in the spintronics.